Until the past few years, printing had been accomplished by the utilization of semicylindrical lead stereos attached to the surface of rotary press cylinders. Modern technology has made possible the utilization of photopolymers to produce thin flexible printing plates. It is extremely desirable to directly replace the cumbersome heavy lead stereos with light-weight saddles that will positively grip and tension flexible polymer printing plates. The problem of attaching flexible members to printing cylinders has traditionally been solved by utilization of complex mechanisms contained within the rotating cylinder. For economic reasons it is preferable to provide a saddle that can be mounted on a conventional cylinder and that will accomplish the same result. The problem has been to positively grip a flexible printing plate within the narrow dimensional confines of saddle thickness. Such a design criteria eliminates the possibility of utilizing bulky mechanical components to produce the clamping forces required. Photopolymer printing plates are generally made by bonding the photopolymer resin to some form of substrate. It is most desirable to positively grip the substrate directly to avoid the problem of photopolymer-substrate separation during press operation. To accomplish this, several manufactures have bonded the photopolymer resin directly to a thin metal backing in order that more conventional clamping of the stronger metal backing could be employed. The instant invention, however, provides positive gripping means within the narrow confines of saddle thickness that will positively grip a flexible substrate. As mentioned before, the prior art has dealt with the problem of attaching a flexible member to a rotating cylinder, as illustrated by U.S. Pat. No. 1,168,498, by utilization of complex mechanical devices within the cylinder. Saddle thickness essentially identical to lead stereo thickness does not allow the luxury of such bulky mechanisms to effect positive clamping. The patent illustrates the use of a roll 8 in combination with a wedge-shape opening 5 to effect clamping. The patent does not show the instant invention which utilizes a plurality of radially and axially moveable sleeves within a wedge-shaped opening, said sleeves individually conforming to the flexible plate yet allowing transverse adjustment of the plate for purposes of color registration.